Suitable compositions and components for photographic developing solutions are well known, and are described for example, in the books Photographic Processing Chemistry by LFA Mason, published by the Focal Press in 1975, any Modern Photographic Processing by G M Haist, published Wiley-Interscience in 1979.
Of recent years, there has been increasing interest in the use of ascorbic acid and related compounds as the agents in photographic silver halide developing solutions. The use of ascorbic acid and related compounds as developing agents is well known, but the recent increase in interest in these developing agents has been prompted by health and safety concerns about other silver halide developing agents.
The use of concentrated photographic developer solutions is also well known. A formulation of a concentrated hydroquinone developer which can be diluted 1:9 before use is given in Haist's book, vol 1, p 528. There is a need, however, for concentrated developers using ascorbic acid as developing agent.
By a concentrated photographic developer we mean a liquid concentrate which has to be diluted with water or other diluent before use, by addition of at least about five parts of water to one part of concentrate (1:5), and preferably by addition of at least about nine or ten parts of water to one part of concentrate. Liquid concentrates are simpler and quicker to dilute than powder formulations, and the greater the dilution factor the less water needs to be transported.
To date, however, a method has not been found for incorporating ascorbic acid or related compounds in concentrated developer compositions. For instance the formulations described in U.S. Pat. No. 5,098,819 are prepared at the final concentration, and not diluted at all.